Driving me crazy, all the other questions here have no proper solution for this.

Is there a solution? I don't really have code to post, as it works fine and dandy accessing the app from any means except the page tab option. That is, the app works fine as a normal iframe app, it's just the page-tab URL is not making the last step.

2 Answers
2

I'm almost 100% sure this is the FBML settings, check both of these settings for the app are not set to FBML - unless you can give us the App ID to check, nobody can give an absolutely 100% sure answer

1) On the 'advanced' tab, the setting for 'canvas mode' - this will not appear for apps created after March 2011

2) There was a setting for 'Page Tab iframe' in the 'Migrations' setting of the Advanced Tab. This controls whether or not FBML is used with the page tabs of your app - if set to disabled, the app is still using FBML for its page tabs

You can also check second setting via the API, for my example app there, the canvas setting can be retrieved via a call to /APPLICATION_ID/?fields=migrations&access_token=APP_ACCESS_TOKEN

The return value is a structure of the migrations the app can set and their values:

Is the 'page tab URL' value you're using relative or absolute? I believe both were supported at one point, try setting it as absolute if it's relative - i'm not sure of the status of that bug report
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IgyMay 30 '12 at 4:12

The URL is absolute. Guess I will have to wait on the FB bug.
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FlavorScapeMay 30 '12 at 21:00

It seems that the pagetab bug is now resolved.
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FlavorScapeJun 14 '12 at 19:35

I just had this problem, the problem was that I had an secure URL (https) in both the canvas and secure canvas. On unsecured connections, the empty rectangle was a result. Both an secure (https) and unsecured (http) URL is required.